Science, Technology and the Environment (SC NATS 1840A) –
Thursday, October 25 , 2012
Readings: 4.4, 4.5 Bulk of test covers Biogeochemical Cycles chapters 6 and 7, 3.3-3.7, 4.4, 4.5, 4.7, same
Biogeochemical Cycles part 3 – Energy Flow
The Sun (Our source of energy)
All of the energy available on Earth comes to us from the Sun.
Facts about the Sun:
Size: 110 x Earth (Diameter)
Mass: 330,000 x Earth
Temp: 6000 degrees (surface) 10^7 degrees (core)
Composition: 90% Hydrogen 10% Helium
Energy source: Hydrogen fusion
Sun’s power output varies continuously, but with some regularity.
11-year sunspot cycle correlated with solar output
Brightness (output) on a long term increasing trend; has probably rise by 25% since protostar
When supply of hydrogen runs out, Sun will die out and become a white dwarf in about 5 billion years.
Earth (our home):
Distance from Sun: 150,000,000 km
Diameter: 12,745 km
Mass: 5.9 x 10^24 kg
Age: 4.6 billion years
Lithosphere: solid rock crust floating on a liquid interior
Hydrosphere: Temperature allows liquid water (71% of surface)
Atmosphere: Mainly nitrogen (78%) and oxygen (21%) Solar Energy Received:
Earth intercepts only a fraction of Sun’s total power output: An average about 1360 W/m^2 (the
solar insolation) at top edge of atmosphere.
Most of this energy is delivered in the form of visible light.
Amount of solar energy that reaches surface and is absorbed by planet also depends on:
Chemical composition of the atmosphere.
Amount of power reflected away from the Earth (or any planet), expressed as fraction of
incident power. Depends on nature of surface and of atmosphere
Albedo = (Power Reflected) / (Power Received)
High albedo more power reflected, less power absorbed, cooler (all else being equal)
Clouds and ice have high albedo; water, rocks, and forests have low albedo.
Earth’s average albedo: about 30%
Chemical Composition of the Atmosphere
A given gas allows EM radiation (light) to pass through at some frequencies, but strongly
Some atmospheric gases strongly absorb the same range of infra-red EM frequencies which the
surface of the Earth Emits as a result of its temperature
Example: Water Vapour, Carbon dioxide, methane, etc…
Ozone in the upper atmosphere also strongly absorbs light at ultra-violet frequencies
The Greenhouse Effect:
Without greenhouse gases average surface temperature would be about 33 degrees colder than
it actually is
Because of atmospheric greenho